The present invention relates generally to sensory feedback devices and, more particularly, the invention relates to sensors for detecting the posture of a human finger and external forces applied to a human finger.
Data gloves have been extensively studied in the past decade in the robotics and virtual reality communities and have been used for a variety of human-machine interactions. There are many ways of providing force feedback to a human from a virtual environment or from sensors on a robot, and many data gloves now make use of such force feedback. External finger forces are traditionally measured by placing sensing pads at the fingertips. However, few data gloves collect external-force data from the human fingers as the human interacts with the environment. To measure the forces acting at the fingers, for example, sensor pads comprising conductive rubber, capacitive sensors, and/or optical detectors can be placed between the fingers and the environment surface. These sensor pads, however, inevitably deteriorate the human haptic sense since the fingers cannot directly touch the environment surface. Moreover, sensor pads may deteriorate or wear out due to mechanical contacts.
Data gloves have also been used to measure the posture or position of human hands and fingers. Another problem presented by data gloves, however, in addition to blocking the natural human haptic sense, is that data gloves cover the fingers restricting the natural bending motion of the fingers.
In accordance with one aspect of the invention, a device for detecting the posture of a finger, the finger having a fingernail illuminated by light, comprises at least one photodetector for measuring a change in light reflected by an area of the finger beneath the fingernail in response to the posture of the finger and providing a signal corresponding to the change in light reflected and a processor for receiving the signal and determining whether the change corresponds to a specified condition. The posture of the finger may be a bent position or an extended position. In a preferred embodiment, the photodetector is an array of photodetectors, the array of photodetectors having a spectral range. The spectral range may include visible and infrared wavelengths.
In another embodiment, the device further includes at least one light source, coupled to the photodetector, the light source for emitting light into the fingernail. In a preferred embodiment, the device further includes a set of light sources coupled to the photodetector, the set of light sources having varying wavelengths and for emitting light into the fingernail. In another further embodiment, the device further includes a housing that encloses the photodetector and a coupling element, connected to the housing, that couples the housing to the fingernail. In a preferred embodiment, the coupling element is a transparent adhesive material.
In accordance with another aspect of the invention, a method for detecting the posture of a finger, the finger having a fingernail illuminated by light, comprises providing at least one photodetector, measuring a change in light reflected by an area of the finger beneath the fingernail in response to the posture of the finger, providing a signal corresponding to the change in light reflected and comparing the change and a specified condition. the posture of the finger may be a bent position or an extended position. The photodetector may be an array of photodetectors having a spectral range. In a preferred embodiment, the method further includes illuminating the fingernail with light from a light source. In an alternative embodiment, the method further includes illuminating the fingernail with a set of light sources having varying wavelengths. The method may further include enclosing the photodetector and the light source in a housing and coupling the housing to the fingernail.
In accordance with another aspect of the invention, an apparatus for detecting a force applied to a finger, the finger having a fingernail illuminated by light includes at least one photodetector for measuring a change in light reflected by an area of the finger beneath the fingernail in response to the force applied to the finger and providing a signal corresponding to the change. The apparatus also includes a processor for receiving the signal and determining whether the change corresponds to a specified condition. In one embodiment, the force applied to the finger is a shear force. In an alternative embodiment, the force applied to the finger is a normal force.